The following disclosure relates to electrical circuits and methods for processing signals.
An often-used circuit applying a bipolar transistor is a current mirror circuit. A current mirror circuit generally serves as a current regulator (or current source), supplying a nearly constant current to one or more loads (or circuits).
FIG. 1 shows a conventional current mirror circuit 100. Current mirror circuit 100 includes a reference current source IREF and a master bipolar transistor Qi, and slave bipolar transistors Q1, Q2, . . . Qn. The bases of master bipolar transistor Qi and slave bipolar transistors Q1, Q2, . . . Qn are commonly connected. Each slave bipolar transistor Q1, Q2, . . . Qn mirrors reference current IREF (i.e., the collector current of master bipolar transistor Qi) to produce output currents I1, I2, . . . In, respectively. Output currents In, I2, . . . In, can be supplied to a variety of electrical circuits represented by circuits 102-1, 102-2, . . . 102-n.
Some current mirror circuits include base current compensation to reduce base current-related errors. Base current-related errors arise due to current loss from a reference current source (e.g., IREF) being reflected at the commonly connected bases of the slave transistors in a current mirror circuit. As shown in FIG. 1, current mirror circuit 100 further includes a compensating bipolar transistor QB that performs base current compensation through a current feedback loop 104. A common problem associated with a current feedback loop, such as current feedback loop 104, is a tendency towards oscillation. To prevent oscillation, a current mirror circuit may include a current source (in addition to the reference current source), and one or more capacitors to stabilize the current feedback loop. For example, current mirror circuit 100 includes capacitors CA and/or CB, and a relatively large current source IC (that increases a gain of bipolar transistor QB and prevents oscillation in current feedback loop 104).